Surface Self-Reconstruction and Sulfidation Strategy to Fabricate Flower-Like NiCo₂S₄ Hollow Nanospheres: Formation, Storage Mechanism, and Application in Hybrid Supercapacitors

In recent years, various hollow structures of NiCo2S4 have been extensively investigated as battery-type electrode materials for hybrid supercapacitors. However, it still remains a challenge for designing a hollow structure with sufficient electroactive sites to improve electrochemical performance. Herein, flower-like NiCo2S4 hollow nanospheres (F-NCS HNSs) were controllably designed and synthesized by integrating a surface self-reconstruction and subsequent sulfidation strategy. Benefiting from the open architecture, the F-NCS HNSs not only have a larger specific surface area to provide more electroactive sites, but also have a highly porous structure to shorten the ion transport path. Meanwhile, the internal hollow structure effectively ensured the structural stability of the electrode material under high current density, significantly improving the electrochemical performance. The obtained F-NCS HNSs exhibited a superior specific capacity (685.2 C g–1 at 1 A g–1), an excellent rate capacity (66.1% from 1 to 30 A g–1), and an extraordinary long-term cycling performance (73.5% at 20 A g–1). In addition, a hybrid supercapacitor was constructed using F-NCS HNSs with activated carbon, which exhibited a high energy density of 47.7 W h kg–1 at a power density of 399.9 W kg–1, and an ultrahigh power density of 7506.0 W kg–1 at an energy density of 29.4 W h kg–1 along with an amazing cycling stability of 92.2% after 10,000 cycles. This work also provides insights for fabricating hollow nanostructure materials for application in other fields.